Some of the richest people in the U.S. are calling for a federal wealth tax.

Financier George Soros, heiresses Regan Pritzker and Abigail Disney and Facebook Inc. co-founder Chris Hughes are among those calling for the levy to help address income inequality and provide funding to address climate change and public health issues.

“We are writing to call on all candidates for President, whether they are Republicans or Democrats, to support a moderate wealth tax on the fortunes of the richest one-tenth of the richest 1% of Americans -- on us,” according to a letter signed by 19 individuals -- one anonymously -- and posted online Monday. “The next dollar of new tax revenue should come from the most financially fortunate, not from middle-income and lower-income Americans.”

Democratic presidential candidates Elizabeth Warren, Pete Buttigieg and Beto O’Rourke support the idea, according to the letter. Warren’s proposal calls for a 2% tax on assets of $50 million or more, and a further 1% on assets over $1 billion. It is estimated to generate nearly $3 trillion in tax revenue over 10 years.

The wealth tax isn’t embraced by all Democrats because many believe it would be difficult to assess objectively the value of wealth like artwork and jewels. There are also concerns that such a tax is unconstitutional because the federal government is prohibited from taxing property, only income.

The New York Times reported on the letter earlier Monday.